In the manufacture of records such as audio records or the newer type of video disc, the initial step in the manufacturing process is to cut a recording of the information desired into a recording substrate. Recordings for audio records are generally cut into a wax or lacquer substrate. Other types of records which have smaller signal elements, such as video discs, are generally cut into metal substrates.
The recorded substrate is then replicated in a matrixing process. The surface of a wax or lacquer recording substrate is activated and then a thin layer of a conductive material is applied to the surface of the substrate as, for example, by electrolytic plating. Thereafter, a metal, typically nickel, is electrodeposited on the recorded substrate until a predetermined thickness of metal is deposited. The electroformed part thus prepared is separated from the wax or lacquer substrate and is used as a master in the subsequent matrixing steps.
The procedure which is used for making replicas from metal recording substrate is slightly different. The surface of the metal recording substrate is passivated to prevent the adhesion of electroplated metal to the metal substrate. Thereafter, a metal such as nickel, is electrodeposited on the surface of the metal recording substrate. When a sufficient thickness of metal has built up on the substrate the resulting electroformed part is separated from the metal recording substrate and is thereafter used as the master in subsequent matrixing steps.
Once the masters are obtained, the matrixing processes employed for further replication are generally similar for various types of records. The masters are mounted on revolvable cathode masks or back plates in an electroforming apparatus. The cathode mask with the master secured to it is immersed into the electrolyte solution and revolved in the solution while a metal is electroformed onto the master. The metal is electroplated onto the master until sufficient thickness of metal is deposited to provide an electroformed part referred to as a mold or mother. The mothers are in turn replicated in an additional electroforming step to form a new series of parts referred to as stampers. The stampers are subsequently used in the pressing of records.
A number of problems have been encountered in the matrixing processes. When the masters are mounted on the revolving back plate to form a mother or when the mothers are mounted on a revolving back plate to form a stamper, it is extremely important that the part which is to be replicated, hereinafter referred to as the matrix, be properly positioned and sealed in a liquid tight fit to the back plate. The matrix must be mounted flush onto the back plate. The outer edge and the center hole of the matrix must be sealed liquid tight to the back plate to prevent electrolyte from flowing behind the matrix.
The problems presented when sealing the center hole are much more difficult to overcome than those presented when sealing the outer edge of the matrix or the back plate since the electrical contact of the cathode to the matrix is made at the center portion of the matrix. The center portion of the matrix should be in full flush contact with the exposed metal surface of the cathode. If full contact is not established and maintained at the center portion, high electrical resistance develops which causes burn outs and treeing about the center hole. The problems encountered in making good electrical contact between the cathode and the matrix are made more difficult because of the relatively small area available for making the electrical connection at the center portion of the matrix. Further a liquid tight seal must be made about the center hole or electrolyte, which is used in the plating bath, will flow through the center hole to the reverse side of the matrix causing plating on the back of the matrix, eventual distortion of the matrix, or electrolyte errosion of the matrix, and eventual damage to the screw threads of the attaching knob and stud that attach the matrix to the cathode.
A further problem arises with respect to centering the matrix on the back plate prior to installing the attaching knob. Since the center hole in the matrix must necessarily be of a larger diameter than that of the attaching stud the center hole must be aligned concentric to the stud. This is currently done by eye. Accurate alignment is important to ensure that good electrical contact is made with the cathode and to prevent leakage of plating solution into the center hole. This alignment has proved to be difficult to perform accurately resulting in poor yield and varying quality.